This invention in general relates to a receiver to be used for a mobile phone or the like. More specifically, this invention relates to the receiver and an adaptive equalizer method in the receiver which judges data without utilizing a training sequence for an operation of an adaptive equalizer.
A conventional receiver and adaptive equalizer method will be explained below. For example, in wireless communication such as a mobile phone, a non-ignorable delay wave is occasionally generated in a data symbol due to multipath propagation. If such a delay wave is generated, interference occurs between code symbols. This phenomenon is called as inter-symbol interference. For this reason, an equalizing technique, for example, exists as a receiving technique which overcomes the inter-symbol interference.
FIG. 20 shows a structure of an adaptive equalizer adopted by a conventional receiver. In FIG. 20, legend 1 denotes a received signal input terminal, legend 2 denotes a decision value output terminal, legend 3 denotes an over-sample sampler, legend 100 denotes a symbol rate data output circuit, legend 101 denotes a timing detector utilizing a training sequence, and legend 102 denotes an equalizer utilizing a training sequence.
Operation of this receiver will now be explained. FIG. 21 is a diagram showing a principle of an over-sample by the receiver. For example, FIG. 21 shows an example of 8-time over-sample, namely, the case where sampling is performed eight times with 1 symbol cycle. Here, sampling time is represented by integer numbers, and over-sample timing numbers corresponding to the sampling time are represented by eight numbers from xe2x80x980xe2x80x99 to xe2x80x987xe2x80x99. Namely, in a sequence where the over-sample timing number is xe2x80x9c1xe2x80x9d, data of time xe2x80x989xe2x80x99 are output as symbol data next to time xe2x80x981xe2x80x99. For example, when the equalizer 102 operates based on the double over sampling, data of time xe2x80x985xe2x80x99 are output as over-sample data as symbol data next to time xe2x80x981xe2x80x99 in a sequence where the over-sample timing number is xe2x80x981xe2x80x99. However, a received sequence will be explained as symbol rate data, but over-sample data can be treated by similar concept.
In FIG. 20 and FIG. 21, a received signal is first sampled at predetermined timing by the over-sample sampler 3. Next, the timing detector 101 receives the over-sampled received signal and determines over-sample timing numbers shown in FIG. 21 by utilizing a training sequence which is a known pattern. Next, the symbol rate data output circuit 100 receives the over-sample timing number, and outputs a received sequence of a symbol rate corresponding to this number. Finally, the equalizer 102 utilizing a training sequence receives the received sequence of the symbol rate, and creates a decision value which is an estimated value of a transmission data sequence so as to output the decision value from the decision value output terminal 2.
In such a manner, normally, the receiver, which uses the equalizer 102 utilizing a training sequence, once estimates a position of a training sequence in any manner so as to operate.
Meanwhile, in addition to such an adaptive equalizer utilizing a training sequence, an equalizer which does not require a training sequence exists. This is referred to as a blind equalizer (for example, described in xe2x80x9cLinear Equalization Theoryxe2x80x9d written by Yoichi Sato, Maruzen, 1990). Since a blind equalizer operates without utilizing a training sequence, the above-mentioned process utilizing training can be avoided.
FIG. 22 shows a structure of a conventional receiver using a blind equalizer described in xe2x80x9cSynchronization Establishing System for Equalizerxe2x80x9d written by Masaaki Fujii (Japanese Patent Application Laid-Open No. 6-216810 (1994)) In FIG. 22, legend 1 denotes a received signal input terminal, legend 2 denotes a decision value output terminal, legend 3 denotes an over-sample sampler, legend 111 denotes a received signal storage circuit, legend 102 denotes an equalizer utilizing a training sequence, legends 103A, 103B and 103C denote blind equalizers with UW (unique word) detecting function, legend 104 denotes a UW portion error comparing circuit, and legend 105 denotes an optimum phase selecting circuit. Here, in later explanation, a training sequence and an unique word (UW) are treated as equivalent.
FIG. 23 shows an example of the structure of the blind equalizer 103 with UW detecting function shown in FIG. 22. In FIG. 23, legend 7 denotes a UW detector, legend 8 denotes a received sequence input terminal, legend 13 denotes a blind equalizer, legend 107 denotes an error output terminal, and legend 108 denotes a mask circuit.
Operation of the receiver shown in FIG. 22 will now be explained. At first, a received signal, which is over-sampled by the over-sample sampler 3, is once stored in the received signal storage circuit 111. Next, the received signal storage circuit 111 outputs an N-systemic received sequence, shown in FIG. 21, where over-sample timing number differs, and N-numbered blind equalizers 103A, 103B, . . . , 103C with UW detecting function receive received signals respectively.
Detailed operation of the blind equalizers with UW detecting function will now be explained with reference to FIG. 23. At first, the blind equalizer 13 which received the received sequence outputs a decision value and an error value. The UW detector 7 receives the decision value so as to detect UW and instructs the mask circuit 108 on mask for mask period other than UW detection time. The mask circuit 108 outputs an error value which was received except at mask instructing period.
Next, the UW portion error comparing circuit 104 receives N-numbered pieces of error information from the N-numbered blind equalizers 103 with UW detecting function, and outputs timing corresponding to a received sequence where the error is the smallest. The optimum phase selecting circuit 105 selects a received sequence of a symbol rate from the received signal storage circuit 111 according to the timing instruction from the UW portion error comparing circuit 104, and outputs the received sequence. Finally, the equalizer 102 receives the received sequence, and performs an adaptive equalizer process utilizing a training sequence so as to output a decision value from the decision value output terminal 2.
As mentioned above, in the conventional blind equalizers, an error signal to be used for timing selection is generated. As a result, this is equivalent to the case where the timing detector 101 utilizing a training sequence in FIG. 20 is realized by utilizing the blind equalizers 103A to 103C with UW detecting function in FIG. 22. Namely, decision values of the blind equalizers with UW detecting function are not utilized as a decision value of the adaptive equalizer process.
However, in the conventional receiver described in the above publication, there arises the following problems:
(1) In order that the adaptive equalizer operates, before the adaptive equalizer operates, a position of a training sequence should be known.
(2) Even if the blind equalizers are utilized, the equalizer which has another structure and utilizes a training sequence is required at a later stage.
(3) It is difficult to reproduce stable timing in an environment of inter-symbol interference.
The present invention is devised in order to solve the above problems. It is an object of the present invention to provide a receiver which is capable of reproducing stable timing even in the environment of inter-symbol interference and outputting a decision value in an adaptive equalizer process only using a blind equalizer without utilizing a training sequence, and relates to an adaptive equalizer method in the receiver.
A receiver of the present invention having an adaptive equalizer which judges a transmission data sequence by means of an adaptive equalizer process comprises a sampling unit which samples a received signal at a speed of not less than a symbol rate; a signal sequence distributing unit which distributes the sampled signal to at least one signal sequence with different sampling timing; a plurality of blind equalization units with reliability information which output decision values (symbol sequences) and their reliability information correspondingly to the respective signal sequences without utilizing a training sequence; and a decision value selecting unit which selects an optimum decision value based on the plural pieces of reliability information.
According to the above aspect of this invention, the sampling unit samples a received signal at a speed of not less than a symbol rate, and the signal sequence distributing unit distributes the sampled signal sequence to sequences with different over-sample timing numbers. Thereafter, the blind equalization unit with reliability information receive the distributed signal sequences and perform the adaptive equalizer process so as to output decision data and reliability information. Finally, the decision value selecting unit receives plural pieces of reliability information and the decision data so as to output the decision data with the highest reliability as a decision value.
Further, the blind equalization unit with reliability information include a blind equalization unit which outputs soft decision values to which reliability for each symbol is added; and a reliability accumulation unit which receives the soft decision values per symbol and outputs a cumulative value of the reliabilities as reliability information.
According to this invention, the blind equalization unit receive the received sequence and outputs soft decision values which are obtained by adding reliability components of each symbol are added to the decision values. The reliability accumulation unit accumulates the reliabilities of each symbol of the soft decision values so as to output reliability information. Here, when a lot of reliability components exist in the soft decision values, the reliability information as the cumulative value show a large value.
Further, the blind equalization unit with reliability information include a blind equalization unit which receives the signal sequence and outputs square errors which are generated when data are judged as well as the decision values; and a reliability accumulation unit which outputs a cumulative value of the square errors as reliability information.
According to this invention, the blind equalization unit receive the received sequence and output square errors which are generated when data are judged as well as the decision values. The reliability accumulation unit accumulates the square errors so as to output the cumulative value. Here, as the square error cumulative value is smaller, the reliability becomes higher.
Further, a frequency deviation addition unit which adds a frequency deviation is provided at a stage before the blind equalization unit with reliability information.
The frequency deviation addition unit gives different frequency deviations to the received sequences to be supplied to the blind equalization unit with reliability information so that selection of decision data is effective even at the same over-sample timing number.
Further, a synchronization judging unit, which performs unique word detection in order to obtain synchronization utilizing the decision values output by the plurality of blind equalization units with reliability information so as to detect as to whether being in a synchronous state or in an asynchronous state, is provided.
For example, when two unique words are detected from the decision values and a number of symbols of the unique words matches with a known value, a synchronous state is obtained. Meanwhile, when two unique words are detected and a number of symbols of the unique words does not match a known value, or when one unique words is not detected, an asynchronous state is obtained.
A receiver of next invention having an adaptive equalizer which judges a transmission data sequence by means of an adaptive equalizer process, comprises a sampling unit which samples a received signal at a speed of not less than a symbol rate; a signal storage unit which stores the sampled signal; a blind equalization unit with reliability information which receive a signal sequence from the signal storage unit and outputs decision values and their reliability information without utilizing a training sequence operating at a clock faster than a signal sequence cycle; and a timing control unit which controls time at which the signal sequence is output and operation time of the blind equalization unit with reliability information so as to output decision data with the highest reliability as decision values.
Thus, the sampling unit samples a received signal at a speed of not less than a symbol rate, and the signal storage unit stores the over-sampled received signal. Thereafter, an over-sample timing number indicated by the operation timing control unit is output at specified timing and at a speed faster than the symbol rate. Finally, the blind equalization unit with reliability information receives a received sequence at a speed faster than a symbol rate and outputs reliability information and decision data.
Further, the blind equalization unit with reliability information includes a blind equalization unit which outputs soft decision values to which reliability for each symbol is added; and a reliability accumulation unit which receives the soft decision values per symbol and outputs a cumulative value of the reliability as reliability information.
Thus, the blind equalization unit receives a received sequence and outputs soft decision values which are obtained by adding reliability components of each symbol to the decision values. The reliability accumulation unit accumulates the reliabilities of each symbol of the soft decision values so as to output reliability information. Here, when a lot of reliability components exist in the soft decision values, the reliability information as the cumulative value shows a large value.
Further, the blind equalization unit with reliability information includes a blind equalization unit which receives the signal sequence and outputs square errors which are generated when data are judged as well as the decision values; and a reliability accumulation unit which outputs a cumulative value of the square errors as reliability information.
Thus, the blind equalization unit receives a received sequence, and outputs square errors which are generated when data are judged as well as the decision values. The reliability accumulation unit accumulates the square errors so as to output the cumulative value. Here, as the square error cumulative value is smaller, the reliability becomes higher.
Further, a frequency deviation addition unit which adds a frequency deviation is provided at a stage before the blind equalization unit with reliability information.
The frequency deviation addition unit gives different frequency deviations to received sequences to be supplied to the blind equalization unit with reliability information so that selection of the decision data is effective even at the same over-sample timing number.
Further, length of a channel memory which is a parameter of the blind equalization unit with reliability information and the frequency deviation can be controlled.
The timing control unit forcibly changes a channel memory length which is a parameter of the blind equalization unit with reliability information and frequency deviations given by the frequency deviation addition unit.
Further, a synchronization judging unit which performs unique word detection in order to obtain synchronization using the decision values and making a judgment as to whether being in a synchronous state or in an asynchronous state, is provided.
The synchronization judging unit makes a judgment as to where the receiver is in a synchronous state or in an asynchronous state by utilizing the decision values. As a result, the over-sample timing number of the signal sequence is changed. For example, when the synchronization is not established, intervals between the over-sample timing numbers are distributed thoroughly. Meanwhile, when the synchronization is established, the intervals between the over-sample timing numbers are set finely so that accuracy of the timing synchronization is heightened.
Further, a synchronization judging unit which performs unique word detection in order to obtain synchronization for each of the blind equalization units with reliability information and making a judgment as to whether being in a synchronous state or in an asynchronous state individually, is provided.
Each synchronization judging unit performs unique word detection on the decision data output by the blind equalization unit with reliability information, and outputs the detected results and detection timing. Further, the decision value selecting unit selects a decision value using not only the reliability information but also the unique word detected results and detection timing.
Further, a reproduction timing generating unit which generates a reproduction timing signal based on timing information including output timing of the optimum decision value and the unique word detected result, is provided.
The decision value selecting unit creates timing information including the finally selected timing and unique word detected result. Further, the reproduction timing generating unit outputs a reproduction timing signal based on the timing information to be a reference.
Further, a reproduction timing generating unit which generates a reproduction timing signal based on timing information including output timing of the optimum decision value and the unique word detected result, is provided.
The decision value selecting unit generates timing information including the finally selected timing and unique word detected result. Further, the reproduction timing generating unit outputs a reproduction timing signal based on the timing information to be a reference.
Further, a reproduction timing generating unit which generates a reproduction timing signal based on timing information including output timing of the decision value and the unique word detected result, is provided.
The timing control unit generates timing information including the finally selected timing and unique word detected result. Further, the reproduction timing generating unit outputs a reproduction timing signal based on the timing information to be a reference.
Further, the sampling unit samples a plurality of received signals individually at a speed of not less than a symbol rate.
A plurality of sampling unit are provided, and a frequency of an operation clock of the blind equalization unit with reliability information is given so that a plurality of different received signals are processed.
An adaptive equalizer method according to next invention of judging a transmission data sequence comprises the sampling step of sampling a received signal at a speed of not less than a symbol rate; the signal sequence distributing step of distributing the sampled signal to at least one signal sequence with different sampling timing; the decision value/reliability information output step of outputting decision values and their reliability information correspondingly to the respective signal sequences without utilizing a training sequence; and the decision value selecting step of selecting an optimum decision value based on the plural pieces of reliability information.
According to the above-mentioned aspect of this invention, a received signal is sampled at a speed of not less than a symbol rate by the sampling step. The sampled signal sequence is distributed to sequences with different over-sample timing numbers. Thereafter, at the decision value/reliability information output step, the distributed signal sequences, and decision data and reliability information are output by executing an adaptive equalizer process. Finally, at the decision value selecting step, a plural pieces of reliability information and decision data are received, and the decision data with the highest reliability are output as a decision value.
Further, the decision value/reliability information output step includes the soft decision value output step of outputting soft decision values to which reliability of each symbol is added; and the reliability cumulative step receiving the soft decision values of each symbol so as to output a cumulative value of the reliabilities as reliability information.
At the soft decision value output step, soft decision values which are obtained by adding reliability components of each symbol to the decision values are output, and at the reliability cumulative step, the reliabilities of each symbol of the soft decision values are cumulated so that the reliability information is output. Here, when a lot of reliability components exist in the soft decision values, the reliability information as the cumulative value shows a large value.
Further, the decision value/reliability information output step includes the square error output step of receiving the signal sequence and outputs square errors which are generated when data are judged as well as the decision values; and the reliability cumulative step of outputting a cumulative value of the square errors as reliability information.
At the decision value/reliability information output step, square errors which are generated when data are judged as well as the decision values are output, and at the reliability cumulative step, the square errors are cumulated so that the cumulative value is output. Here, as the square error cumulative value is smaller, its reliability becomes higher.
Further, the frequency deviation adding step of adding a frequency deviation is provided before the decision value/reliability information output step is executed.
At the frequency deviation adding step, different frequency deviations are given to the received sequence so that the selection of the decision data is effective even at the same over-sample timing number.
Further, the synchronization judging step of performing unique word detection in order to obtain synchronization using the plural decision values and making a judgment as to whether or not being in a synchronous state or in an asynchronous state, is provided.
For example, when two unique words are detected from the decision values and a number of symbols of the unique words matches with a known value, the synchronous state is obtained. Meanwhile, when the two unique words are detected and a number of symbols of the unique words does not match with the known value, or when one unique words is not detected, the asynchronous state is obtained.
An adaptive equalizer method according to next invention of judging a transmission data sequence comprises the sampling step of sampling a received signal at a speed of not less than a symbol rate; the signal storage step of storing the sampled signal; the decision value/reliability information output step of receiving a signal sequence stored at the signal storage step and operating at a clock faster than a signal sequence cycle so as to output decision values and their reliability information without utilizing a training sequence; and timing control step of controlling time at which the signal sequence is output and operation time of the decision value/reliability information output step so as to output decision data with the highest reliability as a decision value.
According to the above-mentioned aspect of this invention, a received signal is sampled at a speed of not less than a symbol rate by the sampling step. The received signal over-sampled is stored at the signal storage step. Thereafter, an over-sample timing number which is indicated at the operation timing control step is output at specified timing and at a speed faster than the symbol rate. Finally, at the decision value/reliability information output step, a received sequence is received at a speed faster than the symbol rate, and reliability information and decision data are output.
Further, the decision value/reliability information output step includes the soft decision value output step of outputting soft decision values to which reliability of each symbol is added; and the reliability cumulative step of receiving the soft decision values of each symbol and outputs a cumulative value of the reliabilities as reliability information.
At the soft decision value output step, soft decision values which are obtained by adding reliability components of each symbol to the decision values are output. At the reliability cumulative step, the reliabilities of each symbol of the soft decision values are cumulated so that the reliability information is output. Here, when a lot of reliability components exist in the soft decision values, the reliability information as the cumulative value shows a large value.
Further, the decision value/reliability information output step includes the square error output step of receiving the signal sequence and outputs square errors which are generated when data are judged as well as the decision values; and the reliability cumulative step of a cumulative value of the square errors as reliability information.
At the decision value/reliability information output step, square errors which are generated when data are judged as well as the decision values are output. The reliability cumulative step, the square errors are cumulated so that the cumulative value is output. Here, as the square error cumulative value is smaller, its reliability becomes higher.
Further, the frequency deviation adding step of adding a frequency deviation is provided before the decision value/reliability information output step is executed.
At the frequency deviation adding step, different frequency deviations are given to a received sequence so that selection of decision data is effective at the same over-sample timing number.
Further, length of channel memory which is a parameter at the decision value/reliability information output step and the frequency deviation can be controlled.
At the timing control step, channel memory length which is a parameter of the decision value/reliability information output step and the frequency deviations given at the frequency deviation adding step are changed forcibly.
Further, the synchronization judging step of performing unique word detection in order to obtain synchronization utilizing the decision values and making a judgment as to being in a synchronous state or in an asynchronous state, is provided.
At the synchronization judging step, a judgment is made as to whether the receiver is in a synchronous state or in an asynchronous state by utilizing the decision values. As a result, the over-sample timing number of the signal sequence is changed. For example, when the synchronization is not established, intervals between the over-sample timing numbers are distributed thoroughly, whereas when the synchronization is established, the intervals between the over-sample timing numbers are set finely so that the accuracy of timing synchronization is heightened.
Further, the synchronization judging step of performing unique word detection in order to obtain synchronization in the unit of the decision value/reliability information output step of outputting the decision values and their reliabilities and making a judgment as to whether being in a synchronous state or in an asynchronous state, is provided.
At the synchronization judging step, unique words are detected based on the decision data output from the plural blind equalization units, and the detected results and detection timing are output. Further, at the decision value selecting step, the decision value is selected by using not only the reliability information but also the unique word detected results and the detection timing.
Further, the reproduction timing generating step of generating a reproduction timing signal based on timing information including output timing of the optimum decision value and the unique word detected result, is provided.
At the decision value selecting step, timing information including finally selected timing and the unique word detected results is generated. Further, at the reproduction timing generating step, a reproduction timing signal is output based on the timing information to be a reference.
Further, the reproduction timing generating step of generating a reproduction timing signal based on timing information including output timing of the optimum decision value and the unique word detected result, is provided.
At the decision value selecting step, timing information including finally selected timing and the unique word detected results is generated. Further, at the reproduction timing generating step, a reproduction timing signal is output based on the timing information to be a reference.
Further, the reproduction timing generating step of generating a reproduction timing signal based on timing information including output timing of the decision values and the unique word detected result, is provided.
At the timing control step, timing information including finally selected timing and the unique word detected results is generated. Further, at the reproduction timing generating step, a reproduction timing signal is output based on the timing information to be a reference.
Further, the sampling step samples a plurality of received signals at a speed of not less than a symbol rate individually.
A plurality of received signals are sampled individually, and frequencies of an operation clock of the blind equalizers are given sot hat the plural different received signal are processed.